A. Field of the Invention
The present invention relates to perimetry, and in particular relates to an automated perimeter and a method of automated perimetry for perimetry-related tests and measures, including producing industry standard tests and results.
B. Problems in the Art
Perimetry is a well known area of visual testing. Perimetry generally involves measurements of retinal response relating primarily to the field of vision of a person. Such analysis by an eye care practitioner can be valuable in detecting and diagnosing major blindness-causing diseases, and can assist in treatment of such diseases. The basic concepts and procedures in perimetry testing have been long established and are well known in the art. See, for example, Drance, S. M. and Anderson, D. R. (Eds), Automatic Perimetry in Glaucoma, Grove and Stratton, Inc., Orlando, Fla. (1985); Silverstone, D. E. and Hirsch, J., Automated Visual Field Testing: Techniques of Examination and Interpretation, Appleton--Century-Crofts/Norwalk, Conn. (1986); Haley, M. J. (Ed), The Field Analyzer Primer, (2nd Ed.), Allergan Humphrey, San Leandro, Calif. (1987), which are incorporated by reference herein.
A conventional measurement procedure for perimetry is to have a patient fixate on a location and then signal when visual stimuli are perceived at various locations in the patient's field of view relative to that of the fixation point. If the patient does not perceive stimuli of certain intensities in certain locations, this indicates to the practitioner the possibility of vision-impairing problems.
Until relatively recently, manually operated perimeter instruments were utilized. See Anderson, D. R., Perimetry With and Without Automation, The C. V. Mosby Co., St. Louis, Mo. (1987), for a general discussion of manual perimetry. These instruments presented several difficulties. First, to obtain valid results, a well-trained, experienced technician or practitioner was needed. Furthermore, the testing procedure was usually long and exacting if accurate measures were to be taken. For example, visual stimuli to the patient had to be manually activated by the tester. Results had to be manually recorded by the tester or an assistant. A variety of systems have therefore been developed for automated, as opposed to manual, perimetry. Many of these are well documented and include several patents. See, e.g., Silverstone and Hirsh, supra, pages 53-81 and:
______________________________________ U.S. Pat. No. U.S. Pat. No. ______________________________________ 3,515,466 3,705,003 3,713,386 3,883,235 3,936,164 3,984,156 4,012,128 4,045,130 4,059,348 4,075,657 4,145,123 4,260,227 4,346,968 4,429,961 4,561,738 4,675,736 4,712,894 4,712,895 ______________________________________
In essence, most automated perimeters attempt to allow the machine itself to adaptively (based on responses to previous stimuli) generate visual stimuli and record the patient's response to the stimuli as well as the parameters of the stimuli (e.g., exact location and intensity). This eliminates the manual record keeping and painstaking procedures of manual perimetry.
While many of the present day automated perimeters have advanced the art, problems and deficiencies still exist in this field, examples of which are discussed below.
Typical automated perimeters are large and relatively cumbersome. Size and weight of the machines have been driven somewhat by necessity. Most utilize a hemispherically shaped dome or a relatively large screen to create a defined and controlled viewing surface for the patient. In essence, this dome or screen requires a size larger than the patient's head to present a sufficiently large surface to test the field of view. It must be large enough, or adjustable, to allow both eyes to be measured. Additionally, the perimeter must accommodate both the patient and the operator from functional and comfort standpoints. The patient must be brought to the perimeter and have his/her head fixed and stabilized with respect to the perimeter to obtain accurate readings.
Additionally, the operator must have some way to not only operate the perimeter but to interact with the patient both physically (for head positioning) and verbally (for instructions).
Many present automated perimeters attempt to incorporate, in one device, all of the parts and components for a perimeter system. This would include a large housing containing the dome or screen, and structure to align and stabilize the patient's head, as well as optical, electrical, and electromechanical devices to generate visual stimuli and record the patient's responses in some fashion. Most automated perimeters, therefore, are of a size which makes them basically non-portable; the volume and weight essentially preventing one person from easily moving or transporting the perimeter from location to location within an office, or between buildings. Alternatively, present automated perimeters attempt to place most of the active components at various locations near or around the dome or screen. This results in rather large, bulky housings.
Other problems or deficiencies in the art include the fact that these rather large integrated units require field servicing and calibration. In other words, if some component, no matter how small or non-complex, fails, a service technician must travel to the device itself for servicing. These devices can not be easily taken or shipped to a central location. The practitioner or the office technician can not easily identify and isolate the failed component and replace it or ship it back to a central location for service.
Integrated, automated perimeters also tend to have deficiencies in the physical accommodation of the patient. In other words, these relatively large, non-portable devices require the patient to move up to the device rather than allowing the machine to be moved to the patient. Many times the final orientation of the patient is unnatural and uncomfortable. The perimetry tests, even with automated units, can take several tens of minutes, which makes this problem more acute. An uncomfortable position may be bearable for a few seconds or even minutes, but not for extended periods. It also may materially affect the test results.
Still further, size and configuration of many automated perimeters make it difficult for the practitioner or technician to interact with the patient. This can be particularly important with respect to verifying whether the patient is appropriately positioned to the perimeter and accurately reacting to the testing. For example, it is important to verify that the patient is fixating a known location during testing and that the patient's eye is open during presentation of each of the individual stimuli. Because the patient's head is basically stabilized in an opening to the dome in the relatively large housings of many current integrated perimeters (to allow view of the dome), such verification is difficult because the patient can not be easily viewed.
Some automated perimeters therefore have utilized verification systems which include such things as view holes through which the tester can watch the patient's eye through the housing and/or even video cameras that take a picture of the eye and present it on a monitor for the tester. Other attempts have been made but room for improvement still exists with respect to ease and accuracy of verifying the status of the patient's eye.
Some present automated perimeters do place some of the processing components outside the main perimeter housing or framework. However, these processing components are generally dedicated to the particular perimeter and are not "open" in the sense that they can be used with other types of perimeters.
A still further problem in the art relates to the value of being able to accomplish industry standard testing to obtain industry standard results. Certain automated perimeters which try to reduce the size of the device, or utilize different types of visual stimuli, may not be able to provide such testing and results.